Tube with composite photocathode for conversion and intensification of x-ray images



SHELDON PH Oct. l7,` 1950 E, E. 2,525,832

TUBE wI'n-x couPosIrE o'rocxmon FoR CONVERSION AND INTENSIFICATION 0F X-RAY IMAGES 3 Sheets-Sheet 1 med nb. zo. 194s la md. MM V/ E NP.

Oct. 17 1950 E; E. sHELno 2 525 832 'russ um .conPosn'E Pso'rocmioB Fon CONVERSION mn IumsIFIcA'rIoN or' x-RAY maas Y 3 Sheets-Sheet 2 Filed Fab. 20, 1946 fdnu'd home/JM@ Oct. 17, 1950 E. E. sHELDoN 2,525,832

TUBE wrm courosrm mo'rocAmonE Fon coNvEnsIou um Imsmcxnon or x-xwz mens Filed Feb. 20. 1946 5 Sheets-Sheet 3' an n wm/eo fsu/mez Meza VENyR. ya.. l A frafhQ/EV TUBE WITH COMPOSITE PHOTOCATHODE FOR CONVERSION AND INTENSIFICATION OF X-RAY IMAGES Edward Emanuel Sheldon, New York, N. Y.

Application February 20, 1946, Serial No. 648,991

4 Claims. (Cl. 178-7.2)

This invention relates to an improved method for intensifying images and refers more particularly to an improved method and device for televising images formed by the impingement of X-rays (which term is meant to include other invisible radiations such as gamma rays and the like, and also irradiation by means of particles such as neutrons) on a iiuorescent or other reactive layer. l

One primary object of this invention is to provide a method of reproducing images formed by X-rays whereby sharper and more intensified reproductions can be obtained. This intensification enables the prolongation of uoroscopic examinations since it would be possible to reduce the radiation strength, or conversely, the exposure necessary in radiography may be reduced.

Another object is to provide 'a device for reproducing sharper and more intensified images. the said image being reproduced in proper spatial relationship to the body being investigated, and in a manner that will enable the operator to palpate the body while viewing the said image.

Still another object is to provide apparatus for televising images formed by X-radiations, which apparatus can be quickly and easily manipulated, and will ailord means for using multiple reproducers, for remote observation and photographic purposes, as well as for the magniiication and diminution oi the image of the examined body.

, Other objects of the present invention will become apparent in the course of the following specification.

Present televising devices concerned with the reproduction of X-ray images have been generally unsatisfactory because the threshold of sensitivity of the most sensitive pickup tubes is about .01 millilambert and the light intensities of fluorescent screens range from .001` to .U1 millilambert. In the industrial iield, iluoroscopy has been almost impossible because the images produced when thick bodies are interposed in an X-ray beam cannot be perceived by the eye.

To accomplish the objects of this invention, an X-ray uorescent or reactive layer is coated with an extremely thin photo-emissive layer, and positioned within a specially designed television pickup tube. This combination, when properly executed results in a considerable improvement in efficiency because of the marked gain (two to three fold) in light reaching the photo-emissive layer. The importance of this construction `is clear when it is considered that the most sensi` operation oi approximately .01 millilambert at Y layer from the photo sensitive layer and would cause a marked diffusion and deterioration of the sharpness of the image, making impossible correct diagnosis. The close opposition of the fluorescent and photo-emissive layers, according to this invention, made possible by the positioning of the iluorescent screen inside of the tube overcomes diiiusion of the image and therefore represents another important advantage.

Further improvement in the operation of this new X-ray sensitive pickup tube can be obtained by the use of a thin layer of aluminum or similar material positioned on the surface of the uorescentlayer, nearest the source of radiation, to increase the transfer of light to the photo-emissive layer.

Apparatus employing this new pickup tube. which by reason of the elimination of the usual optical system used in television apparatus would be of the order of 15 inches in length, can be arranged with the reproducing tube and suitable mirrors to reproduce the image immediately to the rear of the pickup tube. This feature not only allows the presentation of the image in the manner most easily correlated with the subject, but makes it possible to examine the patient by palpation under visual control.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawings, by wayoi example only, preferred embodiments oi the inventive idea. i

In the drawings: t

Figure 1 is a cross sectional view cfa television pickup tube showing the position of liuorescent and photo-emissive layers in accordance with this invention;

Figure 2 is a sectional view of the front portion of a pickuptube showing an alternate form of the invention;

Figure 3 is a view similar to Figure 2, in which neutron reactive layers are illustrated;

tive television pickup tube has a threshold ci Figure4 is a diagrammatic sketch illustrating assess-ia one method of mounting the improved pickup tube and the reproducing tube to obtain an image in proper relationship to the object being viewed; and

Figure 5 illustrates one form of apparatus utilizing the features of this invention.

Figure 6 represents a sectional view of the X-ray sensitive television pick-up tube having electron-emissive layer in composite photocathode.

Figure 7 represents a sectional view of the X-ray sensitive television pick-up tube having photocathode with a light transparent separating layer.

Reference will now be made to Figure 1 which illustrates a new X-ray sensitive pickup tube to accomplish the purposes of the invention outlined above. The operation of standard television tubes is believed to be well known and therefore only those portions necessary to a completefunderstanding of this invention will be described. The primary elements of the pickup tube which remain unchanged are the evacuated housing Iii, the semi-conducting element I2, the cathode IQ, the electron multiplier I5, and suitable focusing and defiecting elements for controlling the electron beam I3. The focusing and deflecting elements are not indicated since they are well known and it 1s bel1eved that they would only serve to complicate the illustration. In accordance with this invention, the face Il of housing In must be of a material transparent to the type of radiation to be employed. The fluorescent layer I8, is positioned on the face Il and its surface, away from the face Il, coated with an extremely thin layer I9 of a suitable photo-emissive substance. The fluorescent layer I8 and the photo-emissive layer I9 should be correlated so that under the influence of the particular radiations used, there is obtained a maximum output of emission. More particularly, the fluorescent screen should be composed of a material having its greatest sensitivity to the type of the radiation to be employed and the photo-emissive material, likewise should have its maximum sensitivity to the wavelength emitted by the fluorescent screen. Fluorescent substances that may be used are willemite, zinc sulphide and its derivatives, calcium tungstate, sodium chloride, potassium bromide, or calcium fluoride, and satisfactory photo-emissive materials would be caesium oxide, caesium oxide activated by silver, or rubidium. Much better photo-emissive action, however, will be achieved with an alloyed layer of antimony with caesium oxide or with an alloyed layer of antimony or bismuth with lithium oxide combined with pure metallic particles of silver on its surface or distributed uniformly throughout the layer. In some cases 'it may be advantageous to provide a very thin layer of silver as a supporting membrane. In the construction of photo-emissive layers, it is very important that it be not thicker than the range of the electrons to be released therefrom.

To obtain still more sensitivity it is preferable to employ a mesh screen I 2a at the semi-conducting element I2, the resolving power of which is comparable to that of the fluorescent surface. The size of picture elements in ordinary mesh screen is 1/w to 1/40 of the size of the crystals customarily used for fluorescent screens. Therefore b v enlarging these picture elements to match the fluorescent crystals an improvement of from 3 to 6:1 ir signal to noise ratio can be realized. In addition to the alteration of the picture element size, the focusing and accelerating fields can be modified to increase the velocity of the photo-electrons leaving the photo-emissive layer, and the storage time can be increased to approximately 1/3 of a second, since in medical and industrial work it is not always necessary to follow motion. The scanning rate may be changed in accordance with `the requirements of the case. The reproducing tube should preferably contain a suitably persistent screen to reduce flicker in the reproduced image.

An alternate form of this invention consists of interposing an X-ray reactive layer between the fluorescent layer I8 and the tube face I l. In Figure 6 I show the X-ray sensitive television pick-up tube l@ having composite photocathode consisting of X-ray reactive, electron-emissive layer "I5, fluorescent layer IB and photo-emissive layer I9 within said tube. In this form of the invention the X-rays would liberate electrons from the interposed reactive layer such as lead or bismuth, which in turn would produce a fluorescent image on layer Iii.

Figure 2 illustrates the method of adapting a reflecting layer 26 between a fluorescent layer 28 and the front face 2l of the pickup tube 20. In this adaptation, the layer 26 is preferably of thin aluminum or similar material that will permit X-radiations to pass thru and impinge on the fluorescent layer 28 as heretofore described. The reflecting layer 26, will act to reflect the fluorescent light back through the fluorescent layer to increase the total quantity of light activating the photo-emissive layer 29. Here again the spectral sensitivity of the fluorescent and photoemissive layers should be matched as well as the resolving power of the elements concerned. In some instances it may be advantageous to use a very thin layer of mica absorber between the fluorescent and the photo-emissive layer in order to prevent photo-electrons, released by the X-rays from reaching the photo-emissive layer or semiconducting element. Another important advantage of the use of a very thin layer of mica or f other light transparent substance is the prevention of chemical interaction between the fluorescent and photo-emissive layer which in short time causes inactivation of both latter layers. In Fig. '7 I show the X-ray sensitive television pick-up tube 'II having composite photocathode consisting of the light reflecting layer 26 of fluorescent layer 28, of thin light transparent layer such as for example of mica 'IG separating said fluorescent layer 28 from the photoemissive layer 29. The remaining parts of the X-ray sensitive pick-up tube are the same as described above.

It is not intended to restrict the scope of this invention to the employment of X-ray or gamma radiations with fluorescent or reactive layers but other corpuscular radi-ations and suitable reactive layers are intended to be comprehended. Another form of the invention is therefore illustrated in Figure 3 wherein the fluorescent layer is omitted and in its place is substituted a neutron reactive substance. More particularly the neutron beam used for the internal investigation of a body would pass thru the front face 31 of the pickup tube 3U and strike a neutron reactive layer 3l which layer should preferably contain atoms from the group boron, lithium, uranium, and gadolinium, and be not thicker than the range of the electrons to be liberated. The liberated electrons would then strike a suitable fluorescent layer 32 causing it to iluoresce and activate the photo-emissive layer 39. The remaining portion of the device then operates as previously described.

In present neutron generating devices, it is difficult to prevent the simultaneous generation of X-radiations and in some instances a thick lead shield may be desirable for shielding the pickup tubes, illustrated in Figure 3, from those radiations.

Figure 4 illustrates, dlagrammatically, a preferred method of employing the new pickup tube in accordance with this invention. In this form the pickup tube 50 together with the reproducing tube 5I are laterally disposed within a suitable box 52. The receiving surface 53 of the pickup tube 5U is arranged to face the X-ray source 5l and react to an image produced by the interposition of a body 55 in the radiating beam. The screen 56 of the reproducing tube 5I faces away from the source and the visible image produced thereon is reflected by mirrors 51 and 58 to a position in the rear of the pickup tube 50 and in proper orientation with the image produced on the face 53.

A suitable ground glass screen 59 or an optical system, for viewing the image, may be found desirable in some instances, although it is not intended that they constitute an essential element of the invention. One instance of this character would be to magnify an image that has been re duced in size, electronically, in order to obtain additional intensification.

From the foregoing discussion, it is apparent that the arrangements of the pickup and reproducing tubes enable the operator to accurately correlate the image with the body,r 55, and since the distance between the body 55 and the image is less than arms length, the object or body may be palpated by the operator while 'viewing the image. This advantage is especially important in medical radiology since the precise angle of observation and the image must be readily and easily correlated.` In many instances it may be found desirable to attach a standard fluorescent screen 60 to the box 52 for obtaining a large survey view of the body 55 prior to or after a detailed examination, with the above apparatus.

One form of device embodying the features of this invention is shown in Figure 5. A suitable ray source 6I is positioned in the desired manner and a body 62 is interposed in the beam 63 emanating from the source 6 l. A housing BI contains the pickup and reproducing tubes as described in Figure 4, together with that electronic equipment, which must be in close physicalrelationship with the said tubes. This housing is supported by a rod 65 connected to a suitable device which provides for universal adjustment and positioning of the said housing. Flexible electrical cables 66 and 61 connect the electronic equipment in housing 64 to the control box 58. 'I'he control box 68 houses that electronic equipment necessary to the operation of the device and has suitable controls 59 for adjustment and regulation. As heretofore mentioned, the operation of electronic equipment for such systems is will known and a detailed explanation is believed unnecessary. Another feature of systems of this type is the possibility of employing any number of reproducers or monitors, Figure 5 indicates the manner of employing an additional reproducer, and is illustrated by box Ill and electrical cable 'H connecting the reproducer to the control box 68. A camera l2, is shown focused on the image formed by the reproducing box 10. although it can also be used for remote bbservation.

and more than one secondary reproducer can be used.

In operating this device, the operator, after positioning the ray generator 6| and the body 62, turns on the apparatus, and by means of controls 69 adjusts the intensity and sharpness of the image viewed in opening 'I3 of box E4. A fluorescent screen 1I, shown in broken lines, can first be positioned in front of the body in order to obtain a large survey view. .After having located the particular area of interest in the body 62, the box 64 can be positioned so that that area, of the body 62, in question intercepts the portion of the beam 53 striking the face of the pickup tube.

With the foregoing apparatus it is obvious that the examiner can rapidly move and position the box 64 enabling him to make a more rapid and complete examination. Since the sensitivity of the device in accordance with this invention greatly exceeds that of presently known equipment, it will be possible to decrease the intensity of the radiations employed and proportionally lengthen the duration of present fluoroscopic examinations without the danger of injuring the body by over exposure to these radiations. It is also possible to decrease the exposure time, instead of reducing the radiation strength, which procedure would be preferred in bothmedical and industrial radiography.

Again by reason of the additional sensitivity provided by this invention, thicker materials can be viewed internally with the result thereof immediately available, and Whenever photographic records are necessary, the exposure time can be reduced or the strength of the radiations can be decreased.

Although particular embodiments and forms of this invention have been illustrated, it is understood that modifications may be made by those skilled in the art without departing from the true scope and spirit of the foregoing disclosure.

What is claimed is:

1. Device for intensifying and televising X-ray images, comprising an X-ray source, an X-ray pick-up tube having a composite X-ray sensitive photocathode within said tube consisting of a light reflecting layer transmitting X-rays from said X-ray source, a fluorescent layer adjacent said light reflecting layer on the side opposite to said X-ray source for converting said X-rays into a light image, a light transparent separating layer adjacent said fluorescent layer, a photoemisslve layer receiving light from said nuorescent layer and from said light reflecting layer through said light transparent layer, a semi-conductive storing target for receiving electrons from said photoemissive layer, means within said tube for scanning said target with a beam of electrons, electron multiplying means within said tube, a collecting electrode for feeding said multiplying means with electrons returned from said target, and an output circuit for said tube connected to said multiplying means.

2. Device for intensifying and televising X-ray images, comprising an `Xray source, an X-raj pick-up tube having a composite X-ray sensitiv photocathode within said tube consisting of fluorescent layer for converting said X-rays int a light image, a light transparent separatin layer adjacent said uorescent layer, a phot( emissive layer receiving light from` said flu( rescent screen through said light transparei layer, a semiconductive storing target :for r ceiving electrons from said photoemissive laye means within said tube for scanning said targ with a beam of electrons, electron multiplying means within said tube, a collecting electrode for feeding said multiplying means Awith electrons returned from said target, and an output circuit for said tube connected to said multiplying means.

3. Device for intensifying and televising X-ray images, comprising an X-ray source, an X-ray pick-up tube having a, composite X-ray sensitive photocathode within said tube consisting of a light reflecting layer transmitting X-rays from said X-ray source, a uorescent layer adjacent said light reilecting layer on th side opposite to said X-ray source for converting said X-rays into a light image, a photoemissive layer receiying light, from said fluorescent layer and from said 15 light reecting layer, a semi-conductive storing target for receiving electrons from said photoemissive layer, means within said tube for scan.

ning said target with a beam of electrons, electron multiplying means within said tube, a collecting electrode for feeding said multiplying means with electrons returned from said target and an output circuit for said tube connected to said multiplying means.

4. Device for intensifying and televising X-ray images comprising an X-ray source,' an X-ray pick-up tube having a composite X-ray sensitive photocathode within said tube consisting of a iluorescent layer for converting said X-rays into a light image, and a photoemissive layer receiving light from said iluorescent layer, a semi-conductive storing target for receiving electrons from said photoemissive layer, means within said tube for scanning said target with a beam of electrons,

EDWARD EIWANUEL SHIELDOVN.

REFERENCES CITED The following references are of record in the file of this patent:

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